WASHINGTON -- From the evidence so far, there's no good reason to let the National Security Agency continue its massively intrusive practice of logging our private phone calls. Congress should pull the plug.

I'm not ignoring all the officials, including President Obama, who swear that the NSA's electronic snooping has foiled dozens of terrorist plots and saved untold lives. I'm just listening carefully, and what we're getting is a lot of doublespeak and precious little clarity.

It's important to keep in mind that Edward Snowden, the former NSA contractor who absconded to Hong Kong and started blabbing the spy agency's secrets, has thus far disclosed the existence of two separate clandestine programs. One, known internally as PRISM, involves the international harvesting of emails and other electronic communications. The other involves the domestic collection of phone call "metadata" -- a vast, pointillist record of our contacts and movements.

The NSA's defenders have consistently -- and, I believe, deliberately -- blurred the distinction between the two. When they talk about the would-be terrorists who have been nabbed and the potential devastation that has been prevented, they lump the programs together.

Obama did so in his interview with Charlie Rose. "We are increasing our chances of preventing a catastrophe ... through these programs," he said.

But it is becoming clear that we should consider "these programs" separately. Privacy concerns aside, PRISM at least seems to produce results. Unless we're flat-out being lied to, PRISM -- which does not target Americans -- has produced substantial quantities of useful information about bad people overseas who seek to do us harm.

The phone-call tracking, on the other hand, is a huge infringement on Americans' privacy that has not been shown to have much investigative value, if any.

At a hearing Wednesday, Senate Judiciary Committee Chairman Patrick Leahy, D-Vt., pressed FBI Director Robert Mueller to give an example of a terrorist plot that was discovered solely because of the stockpiled phone data.

Mueller offered just one: The NSA knew of a phone number in East Africa that was associated with terrorists, so analysts ran the number against the phone log database and saw calls to or from a number in California. This connection led authorities to several men in San Diego who allegedly had sent about $8,500 to al-Shabab, a terrorist group in Somalia.

Mueller said that, overall, there had been "10 to 12" cases in which the phone data was "important," but he could name no others in which it was "instrumental."

As Obama has said, we need to find the right balance between privacy and security; more of one implies less of the other. Is keeping petty cash from reaching al-Shabab important enough to justify letting the government snatch and hoard so much of our private information?

I would say no. And I would also question whether, in this case, the NSA database was even necessary.

The NSA already had the suspicious East African phone number. Authorities could have gone to the secret Foreign Intelligence Surveillance Court and obtained a warrant requiring phone companies to turn over all records of U.S. calls to or from that number -- and, when the California connection emerged, calls to and from the San Diego number.

This would have meant jumping through an extra hoop or two. Good. It's not supposed to be easy or convenient for the government to poke around in people's private affairs.

Mueller said the phone data is needed because terrorism investigations involve connecting those elusive dots that everyone keeps talking about. "What concerns me is you never know which dot is going to be key," he said. "What you want is as many dots as you can. If you close down a program like this, you are removing dots from the playing field."

I understand his concern. But the exemplary cases presented so far all involve some initial piece of information from an outside source -- information that sent investigators on a search for dots of a certain kind. In the San Diego case, the dots of anyone who doesn't chat with Somali terrorists were irrelevant.

The phone companies could be asked or instructed to preserve call data for a period of time, say five years. They probably keep it that long anyway. Judges on the surveillance court -- who are not acquainted with the word no -- could issue warrants when the NSA felt like sifting for patterns.

The NSA might be inconvenienced. But I don't believe we would be any less safe.

Eugene Robinson is an associate editor and columnist for The Washington Post. Email him at eugenerobinson@washpost.com. For archived columns, go to www.gwinnettdailypost.com/eugenerobinson.